400 with gas in the oil!

[cyberjyve]

I have a 99 440 with stage 2 cam polished and ported head with a mikuni flat slide carb. I went out to start it and smelled fuel. I found the air box had what appeared to be gas and oil in the bottom (after the last use I had forgot to shut off the petcock). I attempted to start it and when it warmed up it back fired. So I checked the oil and it was mixed with gasoline. Any ideas? Maybe the petcock needed to be off due to the flatslide carb? Any comments would be appreciated! Thanks!

[cosborne]

Maybe bad rings?? I am just guessing. Fuel might be leaking through the rings and getting down into the oil.

[SicRipp83]

your needle in the carb might be sticking open it will cause gas to leak down into the crank case or the air box.

[curious george]

if it smeels bad when running. then yes there is gas in the oil and you need to change it out. and what the post before this one says about the carb.